Only a fraction of the electricity consumed by a data center actually powers information technology (IT) equipment such as servers, storage devices, and networking devices. The rest is either dissipated during power delivery within the data center or consumed by environmental control systems such as Computer Room Air Conditioning (CRAC), chillers, condensers, fans, and so on. The data center Power Usage Effectiveness (PUE), defined as the ratio of the total facility power consumption to the power used by the IT equipment, is a common measure of the data center's efficiency. Many data center have a PUE of approximately 2, indicating that for every watt of power consumed by the data center's IT equipment, one additional watt is consumed to cool and distribute power to the IT equipment.
Data center operators have to balance two competing goals minimizing the energy used by environmental control systems while at the same time ensuring that computer equipment operation is not negatively affected by high temperatures. Heat removal may be important to ensure proper functioning of the data center because high temperatures may significantly increase microprocessor errors and equipment failure. The cost of removing heat can be a major expense of operating data centers.